Moxifloxacin hydrochloride {1-cyclopropyl-7-[S,S]-2,8-diazabicyclo-[4,3,0]non-8-yl)6-fluoro-1,4-dihydro-8-methoxy-4-oxo-3-quinoline carboxylic acid hydrochloride} is known from EP 350733 & EP 550903 and has the following chemical structure.

Moxifloxacin is a fluoroquinolone broad spectrum antibacterial agent, shown to be clinically active against Gram-positive microorganisms including staphylococcus aureus, streptococcus pneumonia, and streptococcus pyogenes; significantly better than those of Sparfloxacin and Ciprofloxacin that was disclosed in EP No 350,733 and EP No 550,903. Moxifloxacin also has activity against Gram-negative microorganisms including haemophilus influenzae, haemophilus parainfluenzae, klebisiella pneumoniae, and moraxella catarrhalis. 
The prior art disclosed in European patent No's EP 350,733, EP 550,903 and EP 657,448 describes the preparation of moxifloxacin hydrochloride involving the condensation of 1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylic acid or its esters with (S,S)2,8-diazabicyclo[4.3.0]nonane in presence of a base and its conversion to hydrochloride at higher temperatures leading to the desired moxifloxacin along with its potential isomer namely (4aS-Cis)-1-cyclopropyl-6-(2,8-diazabicyclo[4.3.0]non-8-yl)-7-fluoro-8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylic acid as a major impurity. As the impurity and moxifloxacin are positional isomers they are difficult to separate. Further, purification of moxifloxacin to remove this isomer results in lower yields thereby increasing the product cost.
U.S. Pat. No. 5,849,752 discloses the monohydrate of moxifloxacin hydrochloride{1-cyclopropyl-7-[S,S]-2,8-diazabicyclo-[4,3,0]non-8-yl)-6-fluoro-1,4-dihydro-8-methoxy-4-oxo-3-quinoline carboxylic acid hydrochloride} (CDCH) and its preparation by treating the anhydrous crystalline form with ethanol/water mixtures.
Moxifloxacin hydrochloride exhibits polymorphism. WO 2004/091619 discloses a new crystalline Form III of moxifloxacin monohydrochloride and processes for making the crystalline form using an alkanol and an antisolvent for precipitation. This patent discloses X-ray powder diffraction patterns, 13C solid state NMR spectra, Differential scanning calorimetry (DSC) thermogram and IR spectrum of the crystalline form III.
However, it is known that polymorphic forms of the same drug may have substantial difference in certain pharmaceutically important properties such as dissolution characteristics and bioavailability as well as stability of the drug. Furthermore, different crystalline form may have different particle size, hardness and glass transition temperature. Thus, one crystalline form may provide significant advantages over other crystalline forms of the same drug in solid dosage form manufacture processes, such as accurate measurement of the active ingredients, easier filtration, or improved stability during granulation or storage. Furthermore, a particular process suitable for one crystalline form may also provide drug manufacturers several advantages such as economically or environmentally suitable solvents or processes, or higher purity or yield of the desired product.
U.S. Pat. No. 5,157,117 discloses (1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylic acid-O3,O4)bis(acyloxy-O)borate and a process for its preparation by reacting ethyl-1-cyclopropyl-6,7-difluoro-8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylate with Boric acid and acetic anhydride in presence of zinc chloride and its conversion to Gatifloxacin hydrochloride.
WO 2005/012285 discloses the process for the preparation of moxifloxacin hydrochloride using a novel intermediate namely (4aS-Cis)-(1-cyclopropyl-7-(2,8-diazabicyclo[4,3,0]non-8-yl)-6-fluoro-8-methoxy-4-oxo-1,4-dihydro-3-quinoline carboxylic acid-O3,O4)bis(acycloxy-O)borate. The disclosure further refers to the preparation of moxifloxacin hydrochloride pseudohydrate and conversion to moxifloxacin hydrochloride monohydrate. The fingerprinting of the novel intermediate, moxifloxacin hydrochloride pseudohydrate and moxifloxacin hydrochloride anhydrous and moxifloxacin hydrochloride monohydrate forms are substantiated using NMR, FTIR and X-ray diffraction analysis.
Prior art processes for the preparation of the Borate complex without use of catalyst has its limitations owing to higher exothermicity during acetylation thereby reducing the reaction purity which is indicated in the lower yields obtained when further converted to moxifloxacin after condensation with nonane and subsequent hydrolysis. Also prior art makes use of triethyl amine as a base required for the condensation step with nonane.
Hence it is a long felt need of the industry to provide a simple, safe and cost effective process that produces moxifloxacin hydrochloride with high product yield and quality.